A problem which persists in the rinsing of mother liquor from separated solids in a decanter centrifuge is to apply a minimum quantity of rinse liquid or wash fluid directly to the solids cake in the dry beach area as far outwardly as possible to insure that the rinse liquid is spread to the solids and not short-circuited around the flight. Most existing rinsing systems direct the rinse liquid onto the free surfaces of the separated solids pile, or the rise liquid is sprayed by nozzles onto the solids pile. Neither method is efficient since the rinse liquid merely contacts the surfaces of the solids pile without permeating and contacting the interior thereof. Also, the exact location and shape of the solids pile is unknown and therefore difficult to direct the rinse liquid thereonto. The discharged solids thus usually contain undesirably high quantities of the mother liquor or an excessive amount of rinse liquid is needed to achieve desired purity.
Minimum rinse flow is desirable since the cost of providing rinse fluid is high; power demand increases with higher rinse rates and the final product should be as dry as possible. Space for dewatering the rinse liquid from the solids on the dry beach is finite.
The present invention discloses a rinsing scheme wherein spaced orifices, extending radially or spirally inwardly from distal portions of the flight along the working surfaces thereof, pass the rinse liquid therethrough after passing through holes provided in the conveyor hub for collection in a chamber formed continuously along the rear or non-working surfaces of the flight.
Depending upon factors to be discussed hereinafter, the rinse liquid is caused to flow directly onto the solids pile which is continuously forming through orifices immediately inwardly the solids pile surfaces and also into the solids pile from more distally disposed orifices submerged by the solids. As the solids cake continues to grow, rinse liquid passes through those orifices now immediately inwardly thereof, insuring separated solids to be discharged with a desired degree of purity.
It should be noted that orifices above the solids (inwardly thereof) also allow rinse liquid to slide down the face of the flight and onto the wedge of solids, further enhancing the purity of the separated solids. Such arrangement precludes the possibility of rinse liquid passing through air or space occasioned possibly by a left hand helix causing the flight to move away from the rinse liquid.